Abaixo está uma instrução que descreve uma tarefa de geração de SQL, combinada com uma entrada que fornece mais contexto sobre os esquemas de tabela disponíveis. Escreva o código SQL que responda adequadamente à solicitação
 ###Instrução: Por quantos anos Frank Gifford e Dan Dierdorf foram comentaristas de cor juntos?
 ###Tabelas: CREATE TABLE keyboard_"feel"_feature_matrix_for_current_models (keyboard_"feel"_feature_matrix_for_current_models_id AUTO_INCREMENT PRIMARY KEY, Model VARCHAR, Graded Hammer (Non GH3) VARCHAR, Graded Hammer Three (GH3) VARCHAR, Natural Wood Keyboard VARCHAR, Synthetic Ivory Keytops VARCHAR) CREATE TABLE historical_list_of_princeton_eating_clubs (historical_list_of_princeton_eating_clubs_id AUTO_INCREMENT PRIMARY KEY, Name VARCHAR, Years of Operation VARCHAR, Location VARCHAR, Historical Photos VARCHAR, Year Clubhouse Constructed VARCHAR, Sign-in/Bicker VARCHAR, Year co-ed VARCHAR) CREATE TABLE tournament_champions (tournament_champions_id AUTO_INCREMENT PRIMARY KEY, Year VARCHAR, Champion (seed) VARCHAR, Score VARCHAR, Runner-up (seed) VARCHAR, Most valuable player VARCHAR) CREATE TABLE list_of_representatives_who_resigned (list_of_representatives_who_resigned_id AUTO_INCREMENT PRIMARY KEY, Name VARCHAR, Party VARCHAR, Date of resignation VARCHAR, Replacement VARCHAR, Notes VARCHAR) CREATE TABLE 1990s (1990s_id AUTO_INCREMENT PRIMARY KEY, Year INT, Network VARCHAR, Play-by-play VARCHAR, Color commentator(s) VARCHAR, Sideline reporter(s) VARCHAR)  
SELECT COUNT Year FROM 1990s WHERE Color commentator(s) = frank gifford and dan dierdorf